This invention relates generally to a ferroresonant transformer, and more particularly to a controlled ferroresonant transformer employed as a constant current source.
Ferroresonant transformers are employed as constant current sources. In general, the operation of ferroresonant transformers are well known. For example, see my U.S. Pat. Nos. 5,886,507 and 5,939,838, the disclosures of which are herein incorporated by reference. Linear inductors as part of the transformer include a steel core, a coil and an air gap. The inductance is determined by the core cross-sectional area, the number of turns, and the length of the air gap. As the power rating of a controlled ferroresonant current source increases, the resonant capacitance, capacitive current, and control inductive current increase, which requires the control inductor to have a lower value. To reduce the inductance of an inductor, the turns need to be reduced or the air gap increased. The cross-sectional area need to be adjusted to maintain an acceptable maximum flux density. A large air gap poses serious thermal problems because of fringing flux, which cuts through the core laminations and the magnet wire at a high loss angle, producing eddy currents that overheat the inductor and reduce efficiency. Increasing the size of the magnet wire will further reduce efficiency.
Accordingly, it is an object of the present invention to provide a ferroresonant transformer employed as a constant current source which overcomes the above-identified drawbacks associated with high power ratings.
In a first aspect of the present invention, a controlled ferroresonant constant current source includes a ferromagnetic core. An input coil is disposed about the core, and the input coil is to be connected to an alternating voltage source. An output coil is disposed about the core and is inductively coupled to the input coil. The output coil is to be connected to a load. A control coil is disposed about the core and is inductively coupled to the output coil. The control coil is to be connected to a switch for regulating the current output of the constant current source. A first capacitor coil is disposed about the core and is inductively coupled to the output coil. The first capacitor coil is to be connected to a capacitor to provide a first resonant sub-circuit having maximum gain. A second capacitor coil is disposed about the core and is inductively coupled to the control coil. The second capacitor coil is to be connected to the capacitor to provide a second resonant sub-circuit to control resonant gain.
In a second aspect of the present invention, a controlled ferroresonant constant current source includes a ferromagnetic core. An input coil is disposed about the core, and the input coil is to be connected to an alternating voltage source. An output coil is disposed about the core and is inductively coupled to the input coil. The output coil is to be connected to a load. A control coil is disposed about the core and is inductively coupled to the output coil. The control coil is connected to a switch for regulating the current output of the constant current source. A first capacitor coil is disposed about the core and is inductively coupled to the output coil. A second capacitor coil is disposed about the core and is inductively coupled to the control coil. A capacitor is connected to the first capacitor coil for providing a first resonant sub-circuit to generate maximum gain, and the capacitor is connected to the second capacitor coil for providing a second resonant sub-circuit to control resonant gain.
An advantage of the present invention is that the output and control inductors may be integrated onto the transformer core.
A second advantage is that two separate resonant sub-circuits may be implemented which both provide maximum gain and control resonant gain.
A third advantage is that low inductance, high current chokes are no longer a limiting factor to increasing the power rating of the current source.
A fourth advantage is simplified wiring between the transformer core and external components.
These and other advantages of the present invention will become more apparent in the light of the following detailed description and accompanying figures.